Carrying capacity is defined as the number of individuals of a certain species that can be sustained indefinitely in a particular area. The Earths capacity to support people is determined both by natural constraints and by human choices concerning economics, environment, culture (including values and politics), and demography. Human carrying capacity is more difficult to estimate than some of the standard demographic indicators, like expectation of life or the total fertility rate, because human carrying capacity depends on populations and activities around the world. Human carrying capacity is therefore dynamic and uncertain. Ecologists have often made use of the concept of carrying capacity in addressing the pressures that populations put on their environments. Many regions are already exceeding their carrying capacity; they cannot produce enough food to support their populations. One region where this is very clear is an enormous swath of equatorial Africa called the Sahel, that is undergoing very rapid desertification. The burgeoning populations of this area are contributing to its desertification by clearing forest for agriculture as well as for firewood. In 1900, 40% of Ethiopia was covered by forest; now only 4% is forested (Cohen, 1995).The world's population will soon reach a level where there will not be enough resources to sustain life, as we know it. During the last half-century, world population has more than doubled, climbing from 2.5 billion in 1950 to 5.9 billion in 1998. There has been more growth in population since 1950 than during the 4 million preceding years since our early ancestors first stood upright (Brown, Gardner, & Halweil, 1999). This unprecedented surge in population, combined with rising individual consumption, is pushing our claims on the planet beyond its natural limits. Many environmental, social, and economic problems either stem from or are increased in magnitude by the overpopulation p...
